1. Field of the Invention
The invention relates generally to semiconductor processing and more particularly to methods of detecting photoresist residues.
2. Description of the Prior Art
In the fabrication of semiconductor devices and structures, photosensitive organic films, commonly referred to as "photoresists," are used in selective doping by ion implantation and in selectively transferring patterns to films. In subsequent process steps, photoresists are commonly subjected to very harsh environments, such as strong acids, high temperatures, ultraviolet radiation, and high energy reactive ions and radicals. A common problem is in how to remove these highly altered photoresist films as completely as is necessary. Since photoresist films are mostly organic polymers, oxidizing agents are commonly used. The photoresist is usually exposed to an oxygen plasma which reduces carbon based polymers to water (H.sub.2 O) and any of several carbon-oxygen molecules (CO.sub.x). Other methods of removing resist include exposing the resist to a strong oxidizing acid, such as concentrated sulfuric acid (H.sub.2 SO.sub.4), hydrochloric acid (HCl), and others. But since the photoresist is often subjected to processes which alter the organic foundations of the polymer, the complete removal of the photoresist can be very difficult because the material has changed its properties. For example, exposing a photoresist film to a beam of arsenic ions results in the implantation of atomic arsenic into the photoresist film. Resist removal processes that oxidize the resist will subsequently leave an arsenic oxide on the surface.
Incompletely stripped photoresist material is called "residue," and is usually undesirable. Residues can later cause an incomplete etch. Removing residue is essential in any thin film and/or device manufacturing process. The size of the resist residues can vary from large enough to be seen with the naked eye, down to the atomic level. Sub-micrometer residues require very complex analytically tools such as scanning electron microscopy (SEM) to be detected, and even these may or may not help an inspector to see all the residues that are large enough to be a source of problems in later steps.